Polycystic Kidney Disease - Pathology

Gross Pathology

• Both kidneys reach enormous size - weights up to 4 kg each
• On cut section: innumerable spherical cysts up to 3-4 cm in diameter distributed evenly between cortex and medulla
• Cysts contain fluid that is clear, turbid, or hemorrhagic (dark brown/green = old blood)
• Normal intervening parenchyma is essentially absent in end-stage disease
• Fibrous bands encapsulate cysts on cut surface; fibrous tissue plasters the capsule

• Smaller cysts giving a sponge-like appearance
• Dilated, elongated channels oriented at right angles to the cortical surface, replacing cortex and medulla uniformly
• Invariably bilateral

Histology / Microscopic Pathology

• Cysts arise from any nephron segment (tubules and collecting ducts); most studies indicate predominantly distal nephron and collecting duct origin
• Cyst lining is variable and often atrophic (flattened cuboidal epithelium)
• Hyperplastic changes are characteristic:
  • (A) Papillary hyperplasia of cyst epithelium - frond-like projections into the cyst lumen
  • (B) Papillary microscopic adenomas form within the cyst wall
• Occasionally, Bowman's capsule gives rise to cysts - in these, glomerular tufts can be seen within the cystic space
• Even in early disease with normal GFR: interstitial fibrosis, pre-glomerular vascular sclerosis (afferent arterioles + interlobular arteries), and macrophage/lymphocyte interstitial infiltrate
• End-stage: tubulointerstitial fibrosis and arteriolar sclerosis are cardinal features; scant normal parenchyma in isolated patches

• Uniform lining of cuboidal cells (reflects collecting tubule origin throughout)
• Uniformly small cysts; elongated channels perpendicular to cortical surface
• Associated liver findings: multiple epithelium-lined hepatic cysts + portal bile duct proliferation (congenital hepatic fibrosis)

Pathogenesis Summary